Internal combustion engines are equipped with one or more fuel injectors for delivering fuel to the engine for combustion. During certain engine operating conditions, it may be desirable to perform more than one fuel injection. For example, a fuel injection event may be split into three separate fuel injections, such as a pilot injection, a main fuel injection, and a post fuel injection. As such, a pilot fuel injection is performed before the main fuel injection, and is provided to address combustion noise and enhance combustion while a post fuel injection is performed after the main fuel injection, and is provided for improved emission control. Thus, multiple split fuel injections may be performed during a single combustion cycle in order to improve engine performance and reduce emissions.
Fuel injectors are controlled by an engine controller, which provides an actuation signal to the injector for each fuel delivery event. Thus, for split fuel injections including a pilot, a main, and a post fuel injection event, three different actuation signals are provided to the injector. However, the inventors herein have recognized some issues with the above fuel injector control. As an example, when a time interval between two injections is short, providing an actuation signal for each injection can result in overlapping signals. Consequently, there is a limit on the minimum duration of the time interval. Thus, when short time intervals are desired, providing separate actuation signals for each injection can cause variability in the amount of fuel delivered and timing of each fuel delivery event. As a result, engine performance and emission control are compromised. Further, the injector cycles through an actuation cycle for each of the split fuel injections. This can cause additional wear and tear on the injector. Still further, as the engine controller is required to generate a signal for each of the split injections, the controller consumes more resources, thereby decreasing the efficiency of the control system.
In one example, the issues described above may be addressed by a method for a fuel injector comprising: controlling an actuator to move an injector needle from a first position to a third position via a second position; delivering a first fuel injection at the second position and a second fuel injection at the third position, and subsequently moving the needle from the third position to the first position via the second position; and delivering a third fuel injection at the second position. In this way, through a single actuation cycle of the injector comprising movement of the injector needle from the first position to third position via second position, and back to first position from third position via second position, three fuel injections may be performed. As a result, control of timing between two injections can be improved.
As one example, a fuel injector assembly may include a fuel injector body including an injector needle movable along a longitudinal axis of the assembly. The injector body may further include a first row of nozzles positioned above a second row of nozzles along the longitudinal axis. The injector needle may comprise a lower annulus cut portion that couples a fuel supply to either first or second row of nozzles based on a displacement of the needle. The fuel assembly further includes one or more retention springs positioned between an upper portion of the needle and the injector body to bias the needle in an upward direction away from the first and second row nozzles. The assembly also includes an actuator, which when activated pushes the injector needle against the force of the retention springs in a downward direction towards the first and the second row nozzles.
When an electric input is not supplied to the actuator, the needle is at rest or first position. At the first position, the annulus portion is above the first and the second row nozzles and therefore, not coupled to either first or second row nozzles. Thus, fuel delivery does not take place. In order to actuate the needle, an electric input may be initiated when the needle is at the first position and the input may be increased to move the needle downwards towards the first row of nozzles. As the needle travels downwards, the annulus portion couples with the first row nozzles at the second position, and pilot or first fuel injection begins via the first row of nozzles. In order to reach the third position, electric input may be further increased. As a result, the actuator may continue to push the needle downwards causing the annulus portion to decouple from the first row nozzles and subsequently couple with the second row nozzles at the third position. When the annulus portion is coupled with second row of nozzles, the needle may be held at the third position coupled to the second row of nozzles (by maintaining constant electrical input) for a desired duration to deliver the main or second fuel injection via the second row of nozzles. After delivering the main injection, the input may be decreased to move the needle back to the first position from the third position. As the input is decreased, the needle starts to move upwards away from the second row of nozzles to the rest position. En route to first position from third position, during the upward movement of the needle, the annulus cut portion is again coupled with the first row nozzles. During this time, post fuel injection is delivered via the first row of nozzles.
In this way, the fuel injector assembly may be operated to deliver a pilot, a main, and a post fuel injection during a single actuation cycle of the injector. By controlling the movement of the injector needle, rate, amount, and timing of each of the fuel injections can be controlled with increased precision. For example, as a desired time interval between a pilot and a main injection decreases, a rate of increase of electrical input provided to the actuator may be increased. As a result, the fuel injector assembly may be operated to achieve a technical effect of performing multiple injections with reduced time interval between any two injections during a single combustion event.
Further, a plurality of sealing rings, such as O-rings, may be provided along the injector body. For example, sealing rings may be provided in between the two rows of nozzles to achieve the technical effect of hermetically sealing the first row of nozzles from the second row of nozzles. Further, one or more sealing rings may be provided above the first row nozzles to achieve the technical effect of reduced dripping between the injector needle and the body when injector is at the first or rest position, for example.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.